In addition to crawling the Internet faster, our new crawler is more efficient at visiting websites. As a result, site owners will notice as much as a 25% reduction in the number of requests and bandwidth consumed by the crawler.
While transitioning to the new crawler over the past few weeks, we had been running both crawlers in tandem. In some cases, this increased the frequency of Yahoo Search requests to websites. Now, with the new crawler in full production, we have turned off the old crawler and site owners should see a much lower crawl load without a loss in content coverage.
With this change of behavior in the crawler, you may see some shuffling of the pages that are included in the index and some changes in ranking as well.
Forum discussion at WebmasterWorld.